1. Field of the Invention
The present invention relates to a cardiac assist system for helping a heart to properly function. More particularly, the invention relates to a cardiac assist system that applies compressive force to assist the heart in properly contracting, and also applies electrical energy to the heart when needed, such as when the heart is fibrillating.
2. Discussion of the Related Art
The human heart is a very complicated organ that relies on both mechanical and electrical operation to properly function. Over time, the electrical pathways in the heart (which sequentially cause the atria and ventricles to contract) may fail, thereby causing the heart to lose its rhythm, which is known as arrhythmia. In that event, the ventricles will contract at improper times, and as a result the quantity of blood output by the heart decreases. In addition, in some failing hearts the heart muscles do not sufficiently contract the ventricles, also resulting in a dangerous reduction in the amount of blood flow. Furthermore, some hearts occasionally fibrillate (i.e., the muscles of the heart rapidly and irregularly contract), resulting in a lack of synchronism between the heart beat and pulse beat. If not remedied, all of these ailments can cause serious problems, including death.
Numerous attempts have been made to assist diseased or failing hearts by applying external pressure directly to the heart. One such example is direct manual compression of the heart by a person's hand during open chest cardiopulmonary resuscitation. Often, however, the patient requires cardiac or circulatory support for extended periods of time, such as hours, days, or even weeks, and it is quite difficult, if not impossible, for medical personnel to apply a rhythmic pulsating pressure for such an extended period of time. Further, it is difficult, if not impossible, to apply by hand a uniform compressing force to a significant portion of the exterior ventricle surface of the heart. Moreover, the chest should not be opened for extended periods of time because of, among other things, the increased risk of infection. As such, manual manipulation of the heart is not a solution to the problem in most cases.
To overcome this problem, different types of mechanical devices have been developed which intermittently apply external pressure directly to the heart. Some of these devices utilize an inflatable liner that surrounds the heart. For example, U.S. Pat. No. 5,119,804 to Anstadt discloses a cup that is provided with an elastomeric liner. The heart is held in place within the liner, which is cyclically inflated and deflated to apply external pressure to the heart.
In addition, it has been found that these inflatable liner devices can act as electrical insulators to insulate the heart from externally applied energy, such as the energy from defibrillation paddles. Therefore, when such a device is in place over the heart (which can be on the order of days or even weeks), the heart in many instances cannot be defibrillated, if the need arises. It is believed that the polymer material of the liner device, and the air in the liner when it is inflated, act as insulators around the heart, preventing the defibrillation current from reaching the heart.
Accordingly, it will be apparent that there continues to be a need for a cardiac assist system that assists the ventricles to contract in a natural and safe manner, and which also can apply electrical energy to the heart, for example in cases where the heart is fibrillating. The present invention addresses these and other needs.